Recorder control circuit

ABSTRACT

The disclosed recorder includes a rotating drum containing N lines of characters and N cooperating hammers and control windings. Incoming character representing signals are stored in a lesser number of reuseable character register-comparators and compared with the drum position to establish hammer operating times. The windings are connected in a matrix with different groups of windings controlled by different silicon controlled rectifiers and with the register-comparator units coupled in multiple or parallel to windings in the different groups. The rectifiers are enabled in timed sequence, and the registercomparator units apply timed drive potentials to the common windings and rectifiers so that only the rectifiers in the enabled group conduct and energize the coupled windings.

United States Patent 72] Inventor John Guzak, Jr.

Arlington Heights, Ill. [21] Appl. No. 799,740 [22] Filed Feb. 17, 1969 [45] Patented Dec. 14, 1971 [73] Assignee SCM Corporation New York, NY.

[54] RECORDER CONTROL CIRCUIT 12 Claims, 2 Drawing Figs.

[52] US. Cl 307/252 H, 101/93 C, 307/252 K, 317/137, 317/139 [51] Int. Cl ..l l03k 17100, H03k 17/56 [50] Field of Search 307/252, 5O, 51, 53, 90, 243;3l7/137, 139; 101/93 C [56] References Cited UNITED STATES PATENTS 3,243,665 3/1966 Fayer et al'. 317/137 3,423,641 l/l969 Von Feldt 3,46l,796 8/1969 Belson el al.

ABSTRACT: The disclosed recorder includes a rotating drum containing N lines of characters and N cooperating hammers and control windings. Incoming character representing signals are stored in a lesser number of reuseable character registercomparators and compared with the drum position to establish hammer operating times. The windings are connected in a matrix with different groups of windings controlled by different silicon controlled rectifiers and with the registercomparator units coupled in multiple or parallel to windings in the different groups. The rectifiers are enabled in timed sequence, and'the register-comparator units apply timed drive potentials to the common windings and rectifiers so that only the rectifiers in the enabled group conduct and energize the coupled windings.

lll llllll Patented Dec. 14,- 1971 GA. l 3! COUNTER.

M JOHN GUZAK,JR.

RECORDER CONTROL cmcurr BACKGROUND. OF THE INVENTION This invention relates to a data recorder and, more particularly, to a new and improved recorder control circuit for selectively and sequentially controlling the operation of recording elements.

Page or line recorders or printers commonly use a number of series of recording characters on a moving drum or type bar adjacent to which are disposed corresponding print hammers. The characters to be recorded are stored and compared with recording character positions, and the hammers are operated when the desired recording character reaches a recording position. The hammer. control circuits now in use are somewhat complex and require an excessive number of components to efiect the selection of the desired hammer with the desired timing.

SUMMARY OF THE INVENTION A recorder control circuit embodying the present invention can be used with a rotating drum having a plurality of lines of recording characters with corresponding print hammers controlled by individual windings. The control includes a number of character register-comparator units less than the number of hammers which repeatedly store consecutive received characters and compare the stored characters with drum position to determine when the corresponding characters are stored and in printing position. At this time, the register-comparator units deliver a record or record enabling signal.

To control the operation of the hammers, the individual hammer control windings are connected at one end in different groups to differentsilicon controlled rectifiers and the other ends of the windings are connected to timing circuits controlled by the record signals from the register-comparator units, the timing circuits being coupled to a winding in each of the different groups. A sequencing or counting circuit operated in synchronism with the storage of successive sets of characters in the register-comparator units supplies a gate signal to the rectifiers in the different groups in sequence so that the windings or rectifiers are selectively energized in sequence by the coincidence of the gate enabling signal and the record signal.

BRIEF DESCRIPTION OF THE DRAWINGS Many other objects and advantages of the present invention will become apparent from considering the following detailed description in conjunction with the drawings in which:

FIG. 1 is a circuit diagram illustrating a recorder control circuit embodying the present invention; and

FIG. 2 is a fragmentary schematic perspective view of a recording drum with which the control circuit of the present invention is adapted for use.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more specifically to FIG. 1 of the drawings, therein is illustrated a recorder control circuit which embodies the present invention and which is indicated generally as 10. Although the circuit is adapted for use with many different types of recorders, it is described herein in conjunction with a page or line printer using a rotating drum 12 having eighty separate columns or bands of characters on its periphery adjacent to which are disposed eighty corresponding print hammers 14, each having an individual electrical control or operating winding 16. An index wheel 17 rotating in synchronism with the drum 12 is provided with a pair of pickups 18A and 18B adjacent its periphery to supply signals representing the characters on the drum 12 that are disposed adjacent the print hammers 14 in printing position at any given time.

In general, the recorder with which the control circuit 10 is associated is of the type in which an incoming character or a group thereof is stored and compared with signals from the transducers 18A and 188 to establish a coincidence condition when the character to be recorded corresponds to the character on the drum 12 at the printing position. This coincidence is used to effect the selection and energization of the proper one of the windings I6 and the operation of the corresponding print hammer or recording element 14. More specifically, the recorder includes a group 20 of register-comparator units 21-27 in which are stored consecutive received characters to be recorded. The number of units 21-27 is less than the number of print hammers 14 or characters in a line, and in an illustrative recorder using the BO-character drum 12, 16 register-comparator units are provided. Only the first five 2l25 and the last two 26 and 27 are illustrated in FIG. 1 of the drawings. These units sequentially store the character to be recorded and compare this character with the signals received from the transducing heads 18A and 188 to provide a signal when the desired character is in recording position adjacent the proper one of the hammer elements 14. The number of register-comparator units provided can be varied within desired limits, depending on such factors as desired operating speed of the recorder, but will be less than the total number of characters in the line or the number of print hammers 14.

In accordance with the present invention, the output or record signals from the group 20 of register-comparator units is used to control the selective energization of a plurality of silicon controlled rectifiers or controlled conduction devices which energize control windings 16 for the print hammers 14. In FIG. 1, for example, a set 30 of four rectifiers 31, 32, 33, and 34 are provided, the anodes of which are each connected to one terminal of four-windings 16. The rectifier 31 is connected to one terminal of a group including the four windings 16 for the first four hammers 14 in the recorder, while the rectifiers 32, 33, and 34 are connected to one terminal of the next three groups of four windings 16 so that the set 30 is connected to a group of the first sixteen windings 16 in the recorder. Since eighty hammers 14 are provided in the recorder, the control circuit 10 includes four additional rectifier sets similar to the set 30 of which only the second set 36 and the fifth or last set 38 are illustrated. Accordingly, the selective connection of the windings 16 to the anodes of the rectifiers effectively divides the eighty windings 16 into five groups, each including sixteen of the windings 16. Although the sets 30, 36, and 38 are shown as including four rectifiers coupled to four windings 16 each, a greater or lesser number of rectifiers can be provided in each set connected or coupled to greater or lesser numbers of windings in dependence on such factors as the number of recording elements 14 and the current conducting capability of the rectifier.

The control circuit 10 selectively renders the five sets, such as the sets 30, 36, and 38, effective in sequence during the reception of the characters comprising the eighty character line under the control of a counter 40 which is advanced stepby-step in synchronism with the receipt and storage of characters in the sixteen register-comparator units forming the group 20. More specifically, the counter 40 provides a more positive output signal on a conductor 41 during the interval in which the first 16 characters of the line are received and stored in the units of the group 20 and recorded by the recorder. Following the recording of the first group of 16 characters, the positive enabling potential is removed from the conductor 41 and applied to a conductor 42 for the recording of the next 16 characters. The counter 40 sequences the application of positive enabling potentials to the output conductors until a positive potential is applied to a conductor 45 during the recording of the last group of 16 characters.

The positive signals supplied to the output leads from the counter 40 are used to control the supply of a first enabling signal or gate current signal to the rectifiers in the various sets 30, 36, 38. More specifically, the circuit 10 includes five circuits, only three of which 50, 51, and 52 are illustrated, and only one circuit 50 is illustrated in detail. The circuit 50 includes a pair of transistors 53 and 54 connected in a Darlington circuit with the base of the transistor 53 coupled through a diode 55 to the conductor 41. When a more positive signal is applied to the conductor 41, the transistors 53 and 54 are placed in a conductive condition so that the gate electrodes of the four rectifiers 31-34 are supplied with gate current or a first enabling signal to selectively permit these rectifiers to be placed in a conductive condition in dependence on the provision of an anode potential. When the more positive potential is removed from the conductor 41, the transistors 53 and 54 rapidly return to a nonconductive state, and the supply of gate current for the four rectifiers 31-34 in the set 30 is removed. In a similar manner, the remaining four circuits including the circuits 51 and 52 selectively supply a first enabling signal or gate current to the rectifiers in the related sets of rectifiers, such as the sets 36 and 38. The circuits such as 50, 51, 52 and their coupled rectifiers such as 31, 32, 33, 34 provide switching means dividing the windings 16 into five groups.

The provision of anode potential for the rectifiers such as the rectifier 31 is provided by a group 60 of 16 separate timing circuits, only the first five 61-65 and the last two 66 and 67 of which are shown in the drawings. The timing circuits in the group 60 are individually coupled to and controlled by the register-comparator units in the group 20 and operateto supply an anode potential to connected ones of the rectifiers through connected ones of the windings when correspondence between a stored character and a drum character is established. The output of each of the timing circuits is connected to one winding 16 and one of the rectifiers in each of the five groups into which the windings 16 are divided by their connection to the rectifiers 31, 32. As an example, the output of the circuit 61 controlled by the first register-comparator unit 21 is coupled to the first winding 16 and the anode of the connected rectifier in each of the five winding groups defined by the five rectifier sets including the sets 30, 36, and 38. The output of the timing circuit 62, as a further example, is connected to the second winding and connected rectifier in each of these five groups of windings.

Referring now more specifically to the construction of the timing circuits in the group 60, the timing circuit 61 is illustrated in detail and includes a pair of transistors 70 and 71 connected to provide a monostable circuit in which the transistor 70 is normally in a conductive state and the transistor 71 is in a nonconductive state so that a timing capacitor 72 is fully charged. An output lead 73 is normally maintained at ground or a reference potential so that a capacitor 74 is normally charged. When coincidence is established between the character in recording position on the drum 12 adjacent the first hammer 14 and the character stored in the unit 21, the conductor 73 rises to a more positive potential, and the capacitor 74 is momentarily effective through a diode 75 to drive the base of the transistor 70 more positive and terminate conduction through this transistor. This drives the base of the transistor 71 more negative so that this transistor is placed in a conductive state and is effective by virtue of the charged capacitor 72 to maintain the base of the transistor 70 at a more positive potential. This maintains the transistor 70 in a nonconductive state for the period required to discharge the capacitor 72. When the capacitor 72 is discharged to a predetermined level, the transistor 70 returns to a conductive state, and the transistor 71 returns to a nonconductive state.

The emitter of the transistor 71 is coupled to the base of a transistor 76 which together with a transistor 77 is connected in a Darlington circuit. Accordingly, when the transistor 71 is placed in a conductive condition, the transistors 76 and 77 are enabled or. conditioned to apply a more positive potential through a diode 16A and the winding 16 "associated with the first print hammer 14 to the anode of the rectifier 31. If this rectifier is supplied with gate current at this time, the rectifier and the transistors 76 and 77 is placed in a conductive condition to energize the winding 16 and operate the associated print hammer 14. When the monostable circuit including the transistors 70 and 71 times out, the transistors 76 and 77 are quickly returned to a nonconductive state by virtue of the diodes 76A and 77A, and a more negative potential is applied to the anode of the rectifier 31 to terminate conduction therethrough in spite of the persistence of the gate current. Thus, the sixteen circuits or switching means such as 61-67 divide the windings 16 into 16 groups different from the five groups formed by the five rectifier sets such as 50, 51.

in operation, the drum 12 is placed in continuous rotation and the transducing heads 18A and 18B continuously supply position indicating signals to all of the register-comparator units 21-27 in the group 20. As message signals are received, successive characters are stored in the units 21-27, and the counter 40 is advanced to a setting in which a more positive potential is applied over the conductor 41 to the circuit 50 so that gate current is provided to only the four rectifiers 31-34 in the first set 30. As soon as coincidence between a stored character in, for example, the unit 21 and the character in recording position on the drum 12 is established, the timing circuit 61 is rendered effective in the manner described above to apply a brief pulse of more positive potential to the anodes of the five rectifiers connected to the collectors of the transistors 76 and 77. Since only the rectifier 31 is now supplied with gate current, this rectifier is placed in a conductive condition, and the winding 16 associated with the first print hammer 14 is energized to operate this hammer and record the desired character. During succeeding revolutions of the drum and as coincidence is established in the remaining fifteen register-comparator units in the group 20, the remaining timing circuits 62-67 are effective to momentarily apply more positive potentials to the five rectifiers connected to the outputs of these timing circuits. Since, however, only the rectifiers in the first set 30 are supplied with gate current, the output signals supplied by the timing circuits 62-67 are effective to cause the recording of only the remaining 15 characters in the first group of 16 characters on the line.

When these first 16 characters have been recorded, the counter or sequencing circuit 40 advances a step to remove the more positive potential from the conductor 41 and thus remove gate current from the four rectifiers 31-34 in the first set 30. At this time, the counter 40 applies a more positive potential to the conductor 42 so that the four rectifiers in the set 36 are supplied with gate current under the control of the circuit 51. Thus, a s the register-comparator units 21-27 which were cleared on recording the previously stored character are supplied with the next 16 characters to be recorded, these characters are recorded by the second group of 16 hammers 14 under the control of the timing circuits 61-67 in the manner described above. The four rectifiers 31-34 in the set 30 are no longer effective to cause recording inasmuch as the enabling signal or gate current previously provided under the control of the circuit 50 has been removed. ln a similar manner, the remaining three groups of 16 characters are recorded as the counter 40 advances through its cycle of operation.

What is claimed and desired to be secured by Letters Patent of the United States is:

l. A control circuit for a recorder having a number of recording characters movable relative to a number N of recording elements, the recorder including a number M of character registers less than said number N for storing characters of a message, the control circuit comprising a number N of windings each having first and second terminals and controlling the operation of one of the recording elements,

a number S of controlled conduction devices having a pair of output electrodes and a control electrode,

circuit means connecting the first terminals of different groups of the windings to one of the output electrodes of different ones of the devices so that all of the N windings are grouped into S different groups by connection to different ones of the S controlled conduction devices,

a potential source,

means coupling the other output electrodes of the controlled conduction devices to the potential source,

a first control circuit coupled to the control electrodes of all of the controlled conduction devices for applying a first enabling signal to the devices in a timed sequence,

and a number M of second control circuits each controlled by one of the character registers and each coupled to the second terminal of one winding in more than one of said groups, each of said second control circuits applying a second enabling signal over the connected windings to the connected output electrodes of the devices so that a device supplied with both of the first and second enabling signals energizes the connected winding to control the operation of the recording element.

2. The control circuit set forth in claim 1 in which the second control circuits are timing circuits for supplying the second enabling signal for a fixed period of time.

3. The control circuit set forth in claim 1 in which the controlled conduction devices are controlled rectifiers having anode, cathode, and gate electrodes,

the first control circuits are coupled to the gate electrodes,

and the second control circuits supply the second enabling signal to the anode-cathode path of the rectifiers.

4. A control circuit for a recorder having a number of recording characters movable relative to a number N of recording elements, the recorder including a number M of character registers less than said number N for storing consecutive characters of a message, the control circuit comprismg a number N of windings each controlling the operation of one of the recording elements,

a number S of controlled conduction devices having a pair of output electrodes and a control electrode, one terminal of each of a number W of windings being connected to one of the output electrodes of one of the devices so that all of the N windings are grouped into S different groups by connection to different ones of the S controlled conduction devices, the numbers S and W each being at least one and the product of S and W being equal to N,

a first control circuit coupled to one electrode of each of the controlled conduction devices for applying a first enabling signal to the devices, the first control circuit applying the first enabling signal to the devices in a time spaced sequence to divide the S different groups into a number X of different sets, the number X being at least one and no greater than S, the product of X and M being equal to N,

a potential source,

means coupling another electrode of the controlled conduction devices to the potential source,

and a number M of second control circuits each controlled by one of the character registers and each coupled to the other terminal of one winding in each of the X different sets, each of said second control circuits applying a second enabling signal over the connected windings to the connected electrodes of the devices so that a device supplied with both of the first and second enabling signals energizes the connected winding to control the operation of the recording element.

5. The control circuit set forth in claim 4 in which the first control circuit is connected to the control electrodes of the controlled conduction devices,

and the second control circuits are connected to one of the output electrodes of the controlled conduction devices.

6. In a recorder having a number N of recording elements,

N windings each controlling one of the recording elements and each having first and second terminals,

a controlled rectifier having two output electrodes and a gate electrode,

first circuit means connecting the first tenninal of the windings together and to one of the output electrodes of the rectifier,

a control circuit coupled to the gate electrode for applying an enabling signal to the gate electrode to condition the rectifier for conduction,

and a plurality of timing circuits each connected to the second terminal of one of the windings for applying an operating potential across the two output electrodes of the rectifier in series with the connected winding to place the rectifier in conduction and energize the connected winding to control the recording element, each of said timing circuits applying the potential for a fixed period of time less than the duration of the enabling signal applied by the control circuit.

7. The recorder set forth in claim 6 including a number of different groups of N 'windings for corresponding different groups of N recording elements,

a controlled rectifier, a first circuit means, and a control circuit for each of said groups of windings,

second circuit means connecting each of the timing circuits to one of the windings in each of the groups of windings,

and a sequencing circuit coupled to all of the control circuits for rendering the control circuits effective in a timed sequence.

8. A control circuit for a recorder having a series of recording characters movable relative to a number N of recording elements, the recorder including a number M of character register-comparator units less than said number N for storing and comparing characters of a message, the control circuit comprising a number of N of windings each having first and second terminals and each controlling the operation of a different one of the recording elements,

a number M of first switching means each controlled by one of the register-comparator units,

.first circuit means coupling each of the first switching means to the first terminals of a group of the windings so that the first circuit means divides the N windings into a number A of first groups of windings,

a number S of second switching means, I

second circuit means coupling each of the second switching means to the second terminal of a group of windings including windings in different ones of the first groups of windings so that the second circuit means divides the N windings into a number B of second groups, each of the windings being included in one and only one of the A first groups and one and only one of the B second groups,

and control means for operating the second switching means in sequence so that the operation of a given second switching means enables the operation of the windings coupled thereto by the various first switching means under the control of the register-comparator units.

9. The control circuit set forth in claim 8 in which the number A is equal to or is a whole number multiple of the number M.

10. The control circuit set forth in claim 8 in which the number B is equal to or is a whole number multiple of the number S.

11. The control circuit set forth in claim 8 in which each of the second switching means includes a plurality of controlled conduction devices each connected to different windings in one of the groups B and enabled in common by the control means 12. A control circuit for a recorder having a series of recording characters movable relative to a number N of recording elements, the recorder including a number M of character register-comparator units less than said number N for storing and comparing characters of a message, the control circuit comprising a number N of electrical controls each controlling the operation of one of the recording elements,

a number M of first switching means each controlled by one of the register-comparator units,

first circuit means coupling each of the first switching means to a different group of the controls so that the first circuit means divides the N controls into a number A of difierent first groups of controls,

a number S of second switching means,

and means for operating the second switching means in sequence so that the operation of a given second switching means enables the various first switching means to operate the controls selected by the given second switching means under the control of the register-comparator units.

t I I0! I III 

1. A control circuit for a recorder having a number of recording characters movable relative to a number N of recording elements, the recorder including a number M of character registers less than said number N for storing characters of a message, the control circuit comprising a number N of windings each having first and second terminals and controlling the operation of one of the recording elements, a number S of controlled conduction devices having a pair of output electrodes and a control electrode, circuit means connecting the first terminals of different groups of the windings to one of the output electrodes of different ones of the devices so that all of the N windings are grouped into S different groups by connection to different ones of the S controlled conduction devices, a potential source, means coupling the other output electrodes of the controlled conduction devices to the potential source, a first control circuit coupled to the control electrodes of all of the controlled conduction devices for applying a first enabling signal to the devices in a timed sequence, and a number M of second control circuits each controlled by one of the character registers and each coupled to the second terminal of one winding in more than one of said groups, each of said second control circuits applying a second enabling signal over the connected windings to the connected output electrodes of the devices so that a device supplied with both of the first and second enabling signals energizes the connected winding to control the operation of the recording element.
 2. The control circuit set forth in claim 1 in which the second control circuits are timing circuits for supplying the second enabling signal for a fixed period of time.
 3. The control circuit set forth in claim 1 in which the controlled conduction devices are controlled rectifiers having anode, cathode, and gate electrodes, the first control circuits are coupled to the gate electrodes, and the second control circuits supply the second enabling signal to the anode-cathode path of the rectifiers.
 4. A control circuit for a recorder having a number of recording characters movable relative to a number N of recording elements, the recorder including a number M of character registers less than said number N for storing consecutive characters of a message, the control circuit comprising a number N of windings each controlling the operation of one of the recording elements, a number S of controlled conduction devices having a pair of output electrodes and a control electrode, one terminal of each of a number W of windings Being connected to one of the output electrodes of one of the devices so that all of the N windings are grouped into S different groups by connection to different ones of the S controlled conduction devices, the numbers S and W each being at least one and the product of S and W being equal to N, a first control circuit coupled to one electrode of each of the controlled conduction devices for applying a first enabling signal to the devices, the first control circuit applying the first enabling signal to the devices in a time spaced sequence to divide the S different groups into a number X of different sets, the number X being at least one and no greater than S, the product of X and M being equal to N, a potential source, means coupling another electrode of the controlled conduction devices to the potential source, and a number M of second control circuits each controlled by one of the character registers and each coupled to the other terminal of one winding in each of the X different sets, each of said second control circuits applying a second enabling signal over the connected windings to the connected electrodes of the devices so that a device supplied with both of the first and second enabling signals energizes the connected winding to control the operation of the recording element.
 5. The control circuit set forth in claim 4 in which the first control circuit is connected to the control electrodes of the controlled conduction devices, and the second control circuits are connected to one of the output electrodes of the controlled conduction devices.
 6. In a recorder having a number N of recording elements, N windings each controlling one of the recording elements and each having first and second terminals, a controlled rectifier having two output electrodes and a gate electrode, first circuit means connecting the first terminal of the windings together and to one of the output electrodes of the rectifier, a control circuit coupled to the gate electrode for applying an enabling signal to the gate electrode to condition the rectifier for conduction, and a plurality of timing circuits each connected to the second terminal of one of the windings for applying an operating potential across the two output electrodes of the rectifier in series with the connected winding to place the rectifier in conduction and energize the connected winding to control the recording element, each of said timing circuits applying the potential for a fixed period of time less than the duration of the enabling signal applied by the control circuit.
 7. The recorder set forth in claim 6 including a number of different groups of N windings for corresponding different groups of N recording elements, a controlled rectifier, a first circuit means, and a control circuit for each of said groups of windings, second circuit means connecting each of the timing circuits to one of the windings in each of the groups of windings, and a sequencing circuit coupled to all of the control circuits for rendering the control circuits effective in a timed sequence.
 8. A control circuit for a recorder having a series of recording characters movable relative to a number N of recording elements, the recorder including a number M of character register-comparator units less than said number N for storing and comparing characters of a message, the control circuit comprising a number of N of windings each having first and second terminals and each controlling the operation of a different one of the recording elements, a number M of first switching means each controlled by one of the register-comparator units, first circuit means coupling each of the first switching means to the first terminals of a group of the windings so that the first circuit means divides the N windings into a number A of first groups of windings, a number S of second switching means, sEcond circuit means coupling each of the second switching means to the second terminal of a group of windings including windings in different ones of the first groups of windings so that the second circuit means divides the N windings into a number B of second groups, each of the windings being included in one and only one of the A first groups and one and only one of the B second groups, and control means for operating the second switching means in sequence so that the operation of a given second switching means enables the operation of the windings coupled thereto by the various first switching means under the control of the register-comparator units.
 9. The control circuit set forth in claim 8 in which the number A is equal to or is a whole number multiple of the number M.
 10. The control circuit set forth in claim 8 in which the number B is equal to or is a whole number multiple of the number S.
 11. The control circuit set forth in claim 8 in which each of the second switching means includes a plurality of controlled conduction devices each connected to different windings in one of the groups B and enabled in common by the control means.
 12. A control circuit for a recorder having a series of recording characters movable relative to a number N of recording elements, the recorder including a number M of character register-comparator units less than said number N for storing and comparing characters of a message, the control circuit comprising a number N of electrical controls each controlling the operation of one of the recording elements, a number M of first switching means each controlled by one of the register-comparator units, first circuit means coupling each of the first switching means to a different group of the controls so that the first circuit means divides the N controls into a number A of different first groups of controls, a number S of second switching means, second circuit means coupling each of the second switching means to a different group of the controls including controls in different ones of the first groups of controls so that the second circuit means divides the N controls into a number B of second groups, each of the controls being included in one and only one of the A first groups and one and only one of the B second groups, and means for operating the second switching means in sequence so that the operation of a given second switching means enables the various first switching means to operate the controls selected by the given second switching means under the control of the register-comparator units. 